Porosimeter and method of using same



G. G. HEBARD POROSIIIETER AND METHOD OF USING SAME Jan. 9, 1951- 2 Sheets-Sheet 1 Filed April 1, 1946 & m m m FIG ATTORNEYS Jan. 9, 1951 G. G. HEBARD POROSIHETER AND METHOD OF .USING SAIE 2 Sheets-Sheet 2 Filed April 1, 1946- E m IMMIHIUIIIIEIEIIII INVENTOR. G G. HEBARD ATTORNEYS Patented Jan. 9, 1951 roaosIME'rEa AND METHOD or USING SAME Glen G. Hebard, Bartlesville, kia., assignor to Phillips Petroleum Company, a corporation of Delaware Application April 1, 1946, Serial No. 658,798

Claims. (CI. 73-38) 1 This invention relates to porosimeters. In one specific aspect it relates to methods and apparatus for determining the effective porosity of core solids. In another specific aspect it relates to simple methods and apparatus involving a minimum of calculation for determining the effective core space in a sample of a consolidated earth formation by a method involving simpler calculations than are necessary in the usual hydrogen porosimeter and which method avoids contaminating the interior of the core with molten or liquid metal or other liquids or solids. It has long been recognized as very important that careful estimates of the effective porosity of formations encountered in well drillinghbe made. From such estimates the fiow, or lack of flow, of a producing formation (including all possible future production) may be determined.

Difliculties have been experienced in the prior art because the operations to determine the effective porosity have either involved complicated calculations involving the gas laws as corrected for imperfect gases or the sample has been contaminated and rendered unfit for further use by injecting mercury or other foreign substances into the core under high pressure. Calculations requiring the use of Van der Waals constants for gases and his equations for variations of 'Boyles law are unsuited for use in the field by the ordinary oil field technician. Oil companies always like to preserve core samples for future tests and checks on the field of operations and such future tests are impossible when'the core is contaminated with mercury or other substances.

The present invention, however, does not contaminate the core and operates at such pressure ranges that very simple calculations based on Boyle's law alone are suflicient, which calculations can be made by any oil field technician. It is not necessary to use special gases such as hydrogen in the present invention as atmospheric air is sufficient.

The term porosity, as used throughout this specification, refers to efiective porosity, which is the only porosity of value in the determining of the future recovery of oil from the formation. Obviously certain forms of vo'canic glass contain a large number of bubbles of air, which makes them quite light, but their effective porosity is nearly zero because the bubbles are not interconnected. Obviously without such interconnection the oil cannot flow out of the formation into the well, so the only porosity that concerns the oil geologists is eifective' porosity.

One object of the present invention is to provide methods and apparatus for determining porosity. I

Anotherobject is to provide methods and apparatus for determining porosity of samples of consolidated matter which do not contaminate the samples with mercury or other substances.

Another object is to provide methods and apparatus for measuring porosity of samples of consolidated matter without requiring the use of complicated calculations such as those involving Van der Waals constants and equations for imperfect gases.

. Another object is to provide methods and apparatus suitable for rapid determination of porosity of cores in the field by the ordinary oil field technician.

Numerous other objects and advantages will be apparent to those skilled in the art upon reading the accompanying specification, claims and drawings:

In the drawings:

Figure 1 is an elevational view with parts broken away to show details of construction of a device embodying the present invention by which the methods of the present invention may be carried out.

Figures 2 to 7 inclusive. are reduced size elevational views of the apparatus shown in Figure 1, showing the manipulation of the apparatus into different positions during the different stages in the practice of the methods of the present invention.

For example, in Figure 1, valves 8, 9 and I0 are open, gages II and I2 read zero, mercury level I3 is at graduation 0 in the large receptacle I4 and at the zero graduation of the small receptacle I5 and there is no core in the enlarged portion I6 of receptacle I5. The graduation divisions in the drawing on receptacles I4 and I5 are calibrated so that equal volumes are represented by each graduation Obviously this is not essential to the operation of the device since diiferent volume graduations would work equally well by multiplying either by a calibration constant to make the units equal. 1

Figure 2 is unchanged from Figure 1, except that container I4 has beenraised until mercury level ll has risen to the top of lip I8 of valve III with the result that the level of mercury at It has fallen to graduation 7.

Figure 3 is exactly the same as Figure 1, except a core or sample of consolidated matter I9 has been placed in chamber I6. Note that mercury level 0 is the same as in Figure 1 which is unnecessary unless it is desired to check against mercury loss.

In Figure 4, the mercury level 20 has been returned to the top of lip I8, but due to the presence of core I9, mercury level 20 is at graduation 4 of receptacle I4.

In Figure 5, the apparatus has been returned to position of Figure 3 and has the same mercury level I3, but it will be noted that valve Ill has now been closed while in the position of Figure 3.

The positions shown in Figures 1 to 5 inclusive are common to both method species of the accuses invention. From the position of Figure the apparatus may be moved into that of Figure 6 to practice method A." Or the apparatus may be moved from the position of Figure 5 into that of Figure 7 to practice method B. In reaching Figure 6 from Figure 5 it will be noted that valve 9 has been closed, that a gas line-2| has been attached to inject gas under double atmospheric pressure. into the top of receptacle ll, that receptacle ll has been adjusted in height until a common mercury level 22 has been established which in the example shown reads 2.3 on the graduations of receptacle l4, and 2.3 on the graduations oi receptacle l5. It will be noted that gages ii and i2 both read one atmosphere of pressure.

To reach the position shown in Figure '7 from Figure 5, it is merely necessary to raise receptacle it until the mercury level in H is above the mercury level in IS by an amount equivalent to one atmosphere pressure. In the example shown in Figure 7 the mercury level 23 in receptacle H is shown a distance of 760 mm. above the mercury level 24 in receptacle l5 which may be determined by comparison with meter stick 25, and as the operation is assumed to be carried out in this case in an atmosphere pressure of 760 mm. the gage I2 (if present) reads One atmosphere of pressure.

In Figure 1, receptacles l4 and I5 are shown connected by rubber tubing 26 which may be secured in any usual manner such as by wire27. Obviously the exact form of apparatus employed and exact materials of construction or means of construction may be varied without departing from the invention, and while I have shown a preferred embodiment of the structure it is obvious that any equivalent apparatus will allow the performance of equivalent methods and be within the terms of the present invention.

I have therefore shown receptacle II as a cylindrical glass vessel, provided with graduations 28 related to the volume. Vessel M has conduits 29, 30 and 3! communicating with the exterior and conduits 29 and 30. ar controlled by valves 8 and 9 respectively, while conduit 3| leads into pipe 26. Any suitable pressure responsive means I i may be used for indicating the pressure in the air space 32 of chamber H, but for pressure indicating means II and I2, I prefer to employ means which do not change the volume of space 32 to any appreciable'degree in registerin pressure of one atmosphere and, therefore, I preferably employ such a pressure gage as a Bourdon gage in which the tube is liquid filled and pressure transmission between the liquid in the gage and air in space 32 is efiected through a flexible diaphragm 33 which results in very little change in the volume of 32. Obviously other known means for measuring pressures of one atmosphere without substantial volume change will be equally valuable in the practice of the invention and even gages involving considerable volume change will be suitable for use in the present invention if it is merely desired to make a more or less rough estimate of the porosity or the volume change of such a gauge is taken into consideration in the calculations.

Receptacle 15 may be a glass thistle tube with a graduated stem I 5, the graduations being indicative of the volume in IS. Obviously the exact shape and volume of enlarged top It is immaterial as the shape does not enter into the calculations and the volume is found by tests in Figure 2. In order to be able to insert core l3 (and by the term core in this specification, I intend to include any solid or consolidated solid) into portion l6 it is necessary that a portion of It b removable. Whether the line of separation between the top and bottom of I6 occurs is immaterial, but I have found the simpl structure shown in Figure l to be effective.

A washer 34 is threaded on stem 15 and contains holes through which bolts 35 extend. A cover plate 36 is provided with holes for receiving bolt 35 and butterfly nuts may be provided to draw the cover down on IS. A sealing ring or gasket 38 is provided for sealing cover 36 to the top of i6 and obviously care must be exercised between Figures 2 and 3, that the volume of chamber 16 is not changed in replacing top 36 if the highest accuracy is to be maintained. However, as the final result of orosity estimates in oil well drilling is merely indicative of what porosity other untested parts of the formation may have, for most purposes the adjustment of nuts 31 and gasket 38 is not necessarily a delicate operation.

Top plate 36 contains pressure gage I2 and valve seat It as it is preferable to so mount them, however they could be worked into the lower portion IS without departing from the invention.

Valve i0 is supported in cooperative relation 7 with seat It by bracket 39 which may be integral with, or attached to top 36 by any suitable means. Thus, when the liquid level reaches the top of the lip IS, the liquid meniscus may be seen from either side of bracket 39.

Operation In order to carry out the methods "A" and 8" mentioned above it is necessary to first calibrate the apparatus with respect to the volume of portion Hi. Top 36 is placed on top of IS in as uniform a manner as possible each time it is attached by observation of the length of the bolt; 36 projecting through nuts 31 or other such means. The apparatus is moved from the position of Figure l to that of Figure 2 by raising H or lowering IE or both. In practice, it is advisable to construct a board with IS and I4 slidably mounted thereon and scale 25 also slidably thereon in close enough juxta-position so that comparison of the level may readily be made. However, the method may be practiced without such equipment.

In Figure 2, H has been raised relative to 15, as in Figure 1, so that mercury level 13, of Figure 1, has now reached level I! which is level with the top of lip l8. Obviously thediiference between graduation 0 and 7 of I4 is equivalent to the volume of zero mark on 15 to the top of lip i8.

Once this volume of IE has been determined the operations shown in Figures 1 and 2 need not be repeated unless desired. I

The two methods A -and B may therefore be said to start in Figure 3 when core I!) is inserted in portion l6 by removing cover 36 and replacing it. For purposes of convenience, mercury level 13 is shown the same as in Figure 1, but obviously any other mercury level may be employed. The operator notes down the value of mercury level i3, or may wait until the position of Figure 5 is reached before noting down the value. Preferably the values in Figures 3 and 5 are both noted as a check on the proper operation of the device, but either measurement is sufli-cient. Until valve I0 is closed, it makes little difference where mercury level I3 is recorded, but at the time valve I0 is closed it is in tube I5 so that room for the complete advance of the mercury is provided in tube I5 to the position shown in Figure 6 or Figure 7.

Core I9 having been inserted in Figure 3, it is then necessary to determine the exterior volume of the core which is done by raising I4 relative to Hi as shown in Figure 4. Mercury does not readily enter the pores, in cores and the slight mercury head between I8 and I9 is insufilcient to overcome the surface tension of the mercury which surface tension keeps the mercury out of the pores of core I9. Therefore, the difference in reading of volume in chamber I4 between that of Figure 2 and Figure 4 is the exterior of volume of the core without relation to its pores. I

Receptacle I4 is lowered relative to I6 into a position such as shown in Figure 5 and the level I3 is noted in chamber I4 and I5. While for the convenience of operation level I3 would probably be selected the same as in Figure 3 it is not necessarily the same. Valve III is then closed.

Final operation of method A If it is desired to follow method A a tube 2I from a source of gas pressure preferably slightly more than one atmosphere above atmospheric pressure is attached at 29 and by manipulating valves 8 and 9, observing gages II and I2, and leveling the mercury at 22 (by raising or lowering receptacle I4 relative to I5) the state of equilibrium shown in Figure 6 is readily obtained. It will be obvious that in Figure 6, one of gages I I or I2 is enough because mercury level 22 will only be the same in both I4 and I5 when the pressure in space 32 equals that in IS. As gage I2 might have more eflfect by varying the volume of chamber I5 to cause an improper reading it is desirable (if only method "A is to vbe used) to eliminate gage I2 completely. In

such case tube plate 3-6 is merely made without any hole for gage I2 and the measurement in 36 may be made with gage II. However, it is useful to have the device capable of practicing several methods and as gages do not change the volume of IE by an appreciable amount, when the final results and the uses thereof are considered, gage I2 may remain while practicing method A.

Obviously to increase the accuracy of the calculations of both method A" and method B it is preferred to have a barometer (not shown) in the vicinity of the present invention and to make the pressure in 32 and I6 in Figure 6 or in IS of Figure 7 exactly twice the barometric pressure rather than to depend on an arbitrary 760 mm. of mercury. This becomes increasingly important with the altitude at which the test is performed.

Final operation of method "B" In the operation of method B everything is the same up to and including Figure 5. Then the operator proceeds from Figure 5 to Figure 7 by merely raising I4 relative to I6 until the difference between mercury levels 23 and 24 is 760 mm. (or whatever number of mm. corresponding to the actual barometer pressure at the vicinity of the test). In such case, gage I2 is again unnecessary and could be eliminated. However an alternative method would be to ignore the distance between 23 and 24 and to rely on the reading of gage I2 to show an increase in pressure of IE equivalent to the barometric pressure in the vicinity. If desired both meter stick 25 and gage I2 may be employed and one reading checked against the other.

In method B gage II is generally of no value as space 32 is at atmospheric pressure. However gage II could furnish a barometric pressure reading if desired, but it is preferred to get barometric readings from a standard type mercury column barometer (not shown).

In Figure 6, only one gage II or I2 is necessary because the common level 22 in I4 and I5 insures that the pressure is the same on both gages II and I2. In Figure 7,- gage II is at atmospheric pressur and gage I2 is at atmospheric pressure plus the pressure of a column of mercury the height or which is measured by scale 25 between 24 and 23, which pressure is easily calculated.

Use of initial pressure different than atmospheric If desired when valve III is closed in Figure 5 a pressure other than atmospheric (higher or lower) may be placed in IS and I4 by adding or subtracting gas respectively through pipe 29. keeping valve 9 and pipe 30 closed and then leveling the liquid at I3. From Figure 5 then either method A or "B" may be practiced ending in Figures 6 or 7 respectively. The calculations are the same as with atmospheric pressure provided the pressure in chamber I6 is increased a known fraction such as by doubling the pressure in I6 or tripling it, or other known fraction, and the proper factor related thereto is used.

Calculations The results may be calculated as follows to determine the porosity of core I9:

Let us call the reading of volume of chamber I4 in Figures 1, 3 and 5 a and the level in tube I5 in the same figures b. The level in I4 in Figure 2 will be designated as c and in Figure 4 will be d. In Figures 6 and 7 the levels in I4 and I5 will be respectively e and f and the distance between 23 and 24 will be a. The following simple calculation may then be made using the data shown in the specific example shown in the drawings:

a=0 units of tube I4 b=0 units of tube I5 c=7 units of tube l4 d=4 units of tube I4 e=2.3 units of tube I4 f=2.3 units of tube I5 g=760 mm.

Volume of chamber I6 and tube I5 from lip I8 to 0 mark: (c-a) =c=V Volume of chamber I6 and tube I5 from lip I8 to 0 mark with core in place=(da) =G=d Volume of core I9 (solids and ineffective pores +efiective pores) =(c-a) -(da) (c-d) VG=C Volume of solids and ineffective pores in core Volume of effective pores in core I9=P Now since in Figures 6 and 7 the pressure in chamber I6 has been exactly doubled the gas volume around the core and in the effective pore space has been reduced by its volume.

This then means that the gas volume in 18 around core and in the effective pores,

Of course if the pressure is tripled instead of being doubled then instead of R=2(e-a) then Referring to sample calculations we have V=ca=70=7 units G=d-a=4-0=4 units C=VG=7-4=3 units R=2(e-a) =2(2.3-0) =4.6 units R=2(fb) =2(2.3-0) =4.6 units P=R-G=4.64=.6 unit Per cent effective porosity= Operation of method 0 As an alternate method of operation valve to can be closed when apparatus is in position shown in Figure 4 and then lower vessel [4 to a position where the liquid level in i5 stands at 0. Now by means of the stationary meter stick measure the difference in levels of liquid in the two receptacles. In this position and as a result of the preceding maneuver the gas trapped in the effective pore space in position of Figure 4 is expanded to the volume in chamber [6 and I5 around the core, plus the effective pore space itself. This resulting reduced pressure in chamber 16 is represented by the barometer reading g -minus the difference in liquid level reading as determined on the meter stick and which will be herein designated as distance h. For the sample conditions set up herein h=760 mm. and therefore this pressure would be 760660.87=99.l3 mm. of mercury. But the final expanded volume by inspection is G+P so by fundamental pressure volume relationships 760P=('760660.87) (G+P) or 760P=99.13G+99.13P. G however has ben determined to be 4.00 units, hence 760P99.l3P=396.52 and Then Per cent porosity:

Having described my invention, I claim! 1. An apparatus for testing porosity comprising in combination a first graduated chamber having a removable and replaceable wall portion for the insertion of a sample the porosity of which sample is to be tested, said first chamber having an orifice in its uppermost portion disposed and constructed so as to be visible from outside said apparatus whereby an operator can see when any liquid in said apparatus is brimming said orifice, a valve disposed to open and close said orifice without changing the total internal volume of said apparatus, fluid pressure responsive means indicating the gage pressure in said first chamber, a second graduated chamber, a flexible conduit connected to said first and second chambers whereby an operator may quickly vary the relative elevations of said chambers and providing communication between said chambers, said second chamber having an air inlet and an air outlet, a valve disposed to open and close said air inlet, a valve disposed to open and close said air outlet, fluid pressure responsive means indicating the gage pressure in said second chamber and a liquid test medium in said chambers and said flexible conduit.

2. An apparatus for testing porosity comprising in combination a first graduated chamber having a removable and replaceable wall portion for the insertion of a sample the porosity of which sample is to be tested, said first chamber having an orifice in its uppermost portion disposed and constructed so as to be visible from outside said apparatus whereby an operator can see when any liquid in said apparatus is brimming said orifice, a valve disposed to open and close said orifice without changing the total internal volume of said apparatus, a second graduated chamber, a flexible conduit connected to said first and second chambers whereby an operator may quickly vary the relative elevations of said chambers and providing communication between said chambers, said second chamber having an air inlet and an air outlet, a valve disposed to open and close said air inlet, a valve disposed to open and close said air outlet, fluid pressure responsive means indicating the gage pressure in said second chamber and a liquid test medium in said chambers and said flexible conduit.

3. An apparatus for testing porosity comprising incombination a flrstgraduated chamber having a removable and replaceable wall portion for the insertion of a sample the porosity of which sample is to be tested, said first chamber having an orifice in its uppermost portion disposed and constructed so as to be visible from outside said apparatus whereby an operator can see when any liquid in said apparatus is brimming said oriflce, a valve disposed to open and close said orifice without changing the total internal volume of said apparatus, fluid pressure responsive means indicating the gage pressure in said first chamber, a second graduated chamber, a flexible conduit connected to said first and second chambers whereby an operator may quickly vary the relative elevations of said chambers and providing communication between said chambers, fiuid pressure responsive means indicating the gage pressure in said second chamber and a liquid test medium in said chambers and said flexible conduit.

4. An apparatus for testing porosity comprising in combination a first graduated chamber having a removable and replaceable wall portion for the insertion of a sample the porosity of which sample is to be tested, said first chamber having an orifice in its uppermost portion disposed and constructed so as to be visible from outside said apparatus whereby an operator can see when any liquid in said apparatus is brimming said orifice, a valve disposed to open and close said orifice without changing the total internal volume of said apparatus, fluid pressure responsive means indicating the gage pressure in said first chamber, a second graduated chamber, a flexible conduit connected to said first and second chambers whereby an operator may quickly vary the relative elevations of said chambers and providing communication between said chambers, and second chamberhaving an air inlet and an air outlet, a valve disposed to open and close said air inlet, a valve disposed to open and close said air outlet and a liquid test medium in said chambers and said flexible conduit.

5. An apparatus for testing porosity comprising in combination a first graduated chamber having a removable and replaceable wall portion for the insertion of a sample the porosity of which sample is to be tested, said first chamber having an orifice in its uppermost portion disposed and constructed so as to be visible from outside said apparatus whereby an operator can see when any liquid in said apparatus is brimming said orifice, a valve disposed to open and close said orifice without changing the total internal volume of said apparatus, a second graduated chamber, a flexible conduit connected to said first and second chambers whereby an operator may quickly vary the relative elevations of said chambers and providing communication between said chambers, fluid pressure responsive means indicating the gage pressure in said second chamber and a liquid test medium in said chambers and said flexible conduit.

6. An apparatus for testing porosity comprising in combination a first graduated chamber having a removable and replaceable wall portion for the insertion of a sample the porosity of which sample is to be tested, said first chamber having an orifice in its uppermost portion disposed and constructed so as to be visible from outside said apparatus whereby an operator can see when any liquid in said apparatus is brimming said orifice, a valve disposed to open and close said orifice without changing the total internal volume of said apparatus, a second graduated chamber, a flexible conduit connected to said first and second chambers whereby an operator may quickly vary the relative elevations of said chambers and providing communication between said chambers, said second chamber having an air inlet and an air outlet, a valve disposed to open and close said air inlet, a valve disposed to open and close said air outlet and a liquid test medium in said chambers and said flexible conduit.

7. An apparatus for testing porosity comprising in combination a first graduated chamber having a removable and replaceable wall portion for the insertion of a samplethe porosity of which sample is to be tested, said first chamber having an orifice in its uppermost portion disposed and constructed so as to be visible from outside said apparatus whereby an operator can see when any liquid in said apparatus is brim- 7 ming said orifice, a valve disposed to open and close said orifice without changing the total internal. volume of said apparatus, fluid pres;ure responsive means indicating the gage pressure in said first chamber, a second graduated chamber, a flexible conduit connected to said firstand second chambers whereby an operator may quickly vary the relative elevations of said chambers and providing communication between said chambers and a liquid test medium in said chambers and said flexible conduit.

8. An apparatus for testing porosity comprising in combination a first graduated chamber having a removable and replaceable wall portion for the insertion of a sample the porosity of which sample is to be tested, said first chamber having an orifice in its uppermost portion disposed and constructed so as to be visible from outside said apparatus whereby an operator can see when any liquid in said apparatus is brim ming said orifice, a valve disposed to open and close said orifice without changing the total internal volume of said apparatus, a second graduated chamber, a flexible conduit connected to said first and second chambers whereby an operator may quickly vary the relative elevations of said chambers and providing communication between said chambers and a liquid test medium in said chambers and said flexible conduit.

9. The method of measuring the porosity of a sample having relatively small pores comprising the steps of placing the sample in an open chamber of known volume, flooding the chamber around said sample with a measured amount of a liquid having sufi'icient surface tension to prevent the liquid entering said pores, and thereby measuring the volume of said sample including said pores, lowering the liquid level to a measured first level in said chamber below said sample, closing said chamber, forcing additional liquid into said chamber to a second level above said first level but below the level of said sample, and determining the gage pressure in said chamber and the volume of liquid between said first level and said second level, from which steps the porosity of said sample is readily calculated.

10. The method of measuring the porosity of a core which comprises determining the bulk volume of a core by immersion thereof in a test liquid to which the core is impermeable and measuring displacement of the test liquid by the core, replacing the liquid surrounding the core with a gas to which the core is permeable while maintaining contact between said liquid and said gas, and applying pressure to the gas through said liquid to produce a decrease in gas volume which i representative of the volume of core material exclusive of the volume of pores therein which communicate with the core surface.

GLEN G. HEBARD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,293,488 Bays Aug. 18, 1942 2,296,852 Horner Sept. 29, 1942 2,323,556 Mattocks July 6, 1943 2,401,101 Pockman May 28, 1946 

